Fig. 4.

Schematic presentation of a 3-compartment model with a double input function. If a labeled metabolite of the tracer enters tissue, the additional signal has to be accounted for in the model. This model includes a second input curve C_M(t) of a metabolite entering tissue and undergoing nonspecific binding. C₁ represents the nondisplaceable compartment of the authentic ligand, C₂ the specific binding of interest, and C₃ metabolized ligand in tissue. C_P(t) and C_M(t) are the input curves of authentic ligand and metabolite, respectively. C_p C_plasma, C_M C_metabolite